The present invention relates to xe2x80x9cactive implantable medical devicesxe2x80x9d as defined by the Jun. 20, 1990 directive No. 90/385/CEE of the Council of the European Communities, and more specifically to pacemaker, defibrillator and/or cardiovertors devices equipped with a data recording and storage function known as a xe2x80x9cHolterxe2x80x9d function.
The Holter function provides for a continuous monitoring of the patient""s cardiac rhythm parameters, as well as storing the so-called xe2x80x9cevent markersxe2x80x9d (for such events as stimulation, detection outside a refractory period, capture, etc.), to evaluate the stability of the parameter(s) for diagnostic and/or therapeutic purposes. An advantage of the Holter function is, in the event of the death of a patient, an analysis of the data collected (i.e., recorded and stored in memory) during the time preceding the death can be used to help determined the cause of death. It is thus possible to determine if the death was or was not cardiac in origin, and, in the case of a death of cardiac origin, the cause, particularly in the case of a defibrillator or cardiovertor. For example, it is important to know if the cardioversion or defibrillation pulses were or were not delivered by the implant, under which circumstances, for how long, what was the response to the pulse(s), etc.
In this respect, reference is made to the article of Grubman et al., entitled xe2x80x9cCardiac Death and Stored Electrograms in Patients With Third Generation Implantable Cardioverter-Defibrillatorsxe2x80x9d, JACC., Vol. 32, No. 4, October 1998, pp. 1056-62, which gives an account of a statistical analysis carried out postmortem in this manner on tens of patients. However, in a certain number of cases the recording data is no longer available, mainly owing to the fact that, to keep the data, it is essential to stop quickly the implant from recording new data after the death. This is because otherwise, the device continues its recording, and, therefore, would replace gradually the relevant data with a flat electrocardiogram, corresponding to the cardiac rhythm data acquired during the period following death. Indeed, being an implanted device, the information storage capacity is limited, typically to a duration of from twenty to thirty minutes, and the recording is made in a first-in, first-out loop, i.e., as long as the recording continues, the most recent data replaces the oldest data.
The above-mentioned article also deplores the absence of data recorded (e.g., an intracardiac ECG recording) in a great number of cases, which leads to an assumption that the death was not the immediate result of a tachyarrhythmia, but without this assumption being able to be corroborated by an analysis of the heartbeat rate before the moment of the death. In the particular cases of the study reported by this article, the authors note that the heartbeat rate data before death was absent in 69% of the cases, and thus the study of the causes of death which need to be carried out are only for the remaining 31% of the population considered.
In addition, the publication WO-A-89/01803 describes a pacemaker, which records the cardiac activity and stops the recording of the data after a certain time if hemodynamic sensors indicate the stop of cardiac circulation. However, the use of sensors of the blood flow is not easy to implement in association with a pacemaker.
It is an object of the invention to overcome the above-mentioned limitations, by providing an active implantable medical device that detects and automatically indicates a situation establishing the death of the patient, and freezes the last acquired recordings of the cardiac information, namely the heartbeat rate data and/or event markers, for the purpose of later analysis.
To this end, the invention is directed to an active implanted medical device, particularly, a pacemaker, defibrillator and/or cardiovertor, including a circuit means for recording cardiac events and/or parameters representative of these events, (commonly known as xe2x80x9cevent markersxe2x80x9d discussed above), and in which the current recorded information of cardiac events replaces that of the oldest acquired information, and a circuit means for inhibiting the recording means, which inhibiting circuit means is able to stop the recording of the cardiac events and/or event markers in the event of an established death of the patient. The data may be continuously recorded, or intermittently recorded, or recorded in some other manner. This device is preferably characterized in that the inhibiting circuit means detects a spontaneous and/or electrostimulated cardiac activity, and a parameter indicative of a patient""s metabolic demand, these two types of detection being advantageously combined so as to operate the inhibiting circuit means to stop the recording only in the event of the detection of an absence of cardiac activity parameter, confirmed by an absence of a parameter indicative of a patient""s metabolic demand. The patient""s metabolic demand parameter is preferably one or both of a patient physical activity parameter and a patient physiological parameter corresponding to patient effort.